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Old 04-23-2008, 01:27 PM   #76
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Hi Cyndi

Your Dad told you correctly. A 'Multiwire' circuit as you are descibing uses the same neutral between the two hot wires. Those hot wires must be connected to opposite busses or 'phases' if you like. This is so that the neutral current returning on the shared neutral from the loads those two hot wires are serving is subtracting on the neutral and not adding ... so that it will not be overloaded.

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However, now I have two slims in each breaker slot. Therefore, I would not want to put a red wire one slim breaker and the black on the other if they are in the same breaker slot...right???? I would want to skip that slim and put the wire in the breaker above that one on a different breaker slot.
Absoluetly correct! Above or below if your panel has two vertical rows of breakers. The slimlines (tandems) you are using are single pole so connection of one hot wire to another slim on a different buss or leg is required. See the below image but note that this panel does not allow tandems to be installed next to each other. So use your imagination and say that it does. One is a slim (tandem) the one across is a full size both are on the same bus stab and the same leg. In order two have a multiwire with shared neutral using slims I would need to install one either above or below the one you see in the image. One hot to each one will result in a multiwire like you are describing.

Multiwires have other requirements one being that your neutrals to all your receptacles must be pigtailed to the receptacle so that if you take out the receptacle you will not break or open the neutral. Doing so and then restoring power to the circuit will place high voltage on the circuit much like a 240 volt branch circuit that has no neutral. This will not be good for the stuff you have plugged in that only wants 120 volts.

My advice is to use full size double pole breakers and you can't screw the opposite leg thing up. Also the new 2008 code requires them and no longer allows using individual breakers to support a multiwire circuit.
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Old 04-23-2008, 05:57 PM   #77
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Great thread you guys. Maybe I missed something, but is there a reason for not using Aluminum feeder? Quite a bit cheaper. I saw the post about the cost.

Ok so tell me about the pictures. Stubbie is that you? Cyndi is that from around your place? I like pictures.
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Old 04-23-2008, 07:01 PM   #78
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jrclen- Just a little bit of heaven on earth here in Washington. We have 20 acres with 45 animals!! A lot of work, and a lot of rewards!!!! Thanks for asking. And Spread the word on the great job Stubbie is doing for me!!!! What a patient guy to help out a Newbie like me!!!!
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Old 04-23-2008, 07:10 PM   #79
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Hi John

Cyndi has a conduit buried already with 3 #8 thwn coppers installed. I haven't asked Cyndi the size of conduit that is in the ground already. An aluminum feeder is a great idea if the conduit will allow it. I was suggesting to just stick with the THWN number 8's and add the ground sized large enough for a 100 OCPD to match her new panel in the event she would ever need that as she expands her animal shelter. Right now she has the #8's on a 40 breaker. She can go up to a 50 breaker and at 140' she will have a reasonable voltage drop though not the best. She has indicated the #8's on the 40 have been getting the job done with her present load demands. So we are going to go up to a 50 and only add the ground #8 to be compliant with the feeder needing to be 4 wires. (Washington State requirement). I suggested #6 copper later on only because I know the conduit is large enough to accept the #6's if copper thwn. If she has 1" PVC then she could get 3 #4 al plus reuse the ground she has ...so your suggestion is warranted knowing the conduit size.

Sorry that is not me....... that is HonkerinMO and AndyInATL. You would have to go back to the HotTub thread to see how they got together but the moderators moved all the good stuff to the off subject area. I think they were jealous of the Romance that got started as we helped Honker fix a faulty gfci breaker.
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Old 04-23-2008, 07:45 PM   #80
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Hey Guys! The conduit is larger than 1" as there is a clearly marked 1" pvc conduit next to it and the one that I ran is larger. It says TC2 #8 on it with a bunch of other stuff but no clear size. So it is at least 1-1/2". Overkill huh???
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Old 04-23-2008, 09:11 PM   #81
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Hi again Cyndi

Sorry stepped out for a burger at my favorite spot. John is correct aluminum is cheaper and it is fine to use for a feeder. The thing to remember is that aluminum needs to be larger than copper. So to have aluminum on a 70 amp breaker like we were talking earlier with #6 copper you will need #4 aluminum XHHW or other wet location insulation. Just look for the W on the wire labeling.

And one point to consider with long runs of electrical wire is voltage drop, using these wire sizes above we are at the teetering edge for a reasonable design at the distances your giving us. If you can install a bigger wire than #4 in aluminum at a price you can afford then by all means do so. A good wire size in aluminum would be #1 awg at 65 amps and 140 feet. That is close to 2% voltage drop on the feeder. The ground will also have to increase in size.

But the conduit has to be large enough so let me post back in a few minutes with that information.
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Old 04-23-2008, 09:20 PM   #82
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Stubbie-I was wrong on the distance from the pole panel to the barn. It is 100 feet plus an additional 10 feet to run up to the panels. Total of 110 feet. Sorry. Cyndi
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Old 04-23-2008, 09:48 PM   #83
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Thats ok Cyndi. 110 feet it is. That brings the copper #8's we are planning closer into the center of the ballpark we are wanting. So lets just stick with that until you get ready to have a bigger feeder to the barn if you need it someday. Right now you are only buying one wire for the ground. We will talk aluminum if you upgrade... unless you are in a change of mind.

The other thing that concerns me is you said you had a 300 foot run of #12 copper out to a pasture. Is that on a multiwire shared neutral or a 120 volt circuit on a single breaker?
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Old 04-23-2008, 10:03 PM   #84
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two circuits/shared neutral.
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Old 04-23-2008, 10:16 PM   #85
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By the way, I had a building inspector come by today for the new building that houses the sub-panel. He didn't even check it. I had the breaker off and was in the process of pulling wire. That got me to thinking, should I have had a permit?
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Old 04-23-2008, 11:50 PM   #86
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Ok Cyndi

Let me see if I can explain this easily. A shared neutral multiwire is just like a 240 volt circuit with no neutral when considering voltage drop....if for example you have a load on each hot wire that is the same in amps and both loads are at the exact same distance from the panel. This is the ideal situation as only the one way distance is calculated in the voltage drop because there is no return current on the neutral or at least very little.
So lets say I had two of your 1200 watt 120 volt heaters at 300 feet in the same water trough. Each heater plugged into gfci receptacles served by the hots wires of the multiwire. If I use a voltage drop calculator it assumes the one way distance of 300 feet to be one half the distance round trip for 120 volts So it calculates the distance to be 600 feet for 120 volts.

The multiwire is serving two 10 amp balanced loads at 300 feet not 600 because current is not returning to the panel over the neutral. So when I enter this into a calculator using 120 volts 10 amps I set the distance to 150 feet so that it will calculate 300 feet not 600. This gives me a drop of 6 volts or 114 volts at each heater if we have 120 volts at the panel. This is a 5% voltage drop. You don't want much more than that on resistive heater loads.

Now in contrast lets just run one heater a 1200 watts (10 amps) on 120 volts 300 feet. When I calculate this I will get a result from a round trip of 600 feet because all the current is traveling on the neutral back to the panel. That will be 12 volts of drop or 108 volts at the heater 10% voltage drop. Notice this is double the drop of a multiwire branch circuit with balanced loads at the same distance.

Now it gets a little trickier when we vary the loads and the loads aren't at the same distances but the voltage drop advantages are still there balanced loads or not.

If however no load is operating on one leg..... for instance lets say you unplug one of those heaters on the multiwire example I gave.. you now have lost all the advantages of the multiwire because you now just have one 120 volt circuit operating and all its current is returning to the panel and source so your at 600 feet of voltage drop instead of 300. The advantage in voltage drop comes when cancellation of the neutral current is occurring when both legs of the multiwire are operating loads.

So if you have multiwires to those heaters in the pasture be sure to have both legs operating something like the heaters and the thermostats set the same. Balance the loads between legs best you can.
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Old 04-24-2008, 09:02 AM   #87
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Cyndi, that is a pretty place. I live way out in the sticks in Wisconsin, I appreciate country views. And I know how well Stubbie does on electrical advise. He is an ace. You're in good hands.

Stubbie, I didn't mean to muddy the waters with the alum feeder. I thought I read a post in the middle about pulling new conductors in to increase the sub panel size. I didn't think that was you in the photo. When I was that young the pictures were all black and white.
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Old 04-24-2008, 11:24 AM   #88
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Morning! I think I get most of what you have explained about voltage drop. I will have to read it over several times before it all makes sense. The Heaters that I have (don't know if there is any other kind) do not have a thermostat that I can regulate. They are simply heaters that you drop into a tank with a waterproof chord that plugs into the receptacle. So if I understand it, they may come on at different times as the temperature changes in each trough causing an unbalanced load. Is that what I should understand. If so, how can I remedy that? Or should I not worry about it at this time? I have till this next winter to get it all right so you tell me what I need and I will get r done!

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Old 04-24-2008, 11:28 AM   #89
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P.S. None of the 4 outside receptacles are gfci. Another change to make!!!!
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Old 04-24-2008, 11:33 AM   #90
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I went out to work on the barn and just in case, I checked the 40 amp breaker at the pole and someone had turned it on!!! Never assume that it is the way that you left it right!!!!!!!!!!!!!!!! I guess the neighbor wanted to see the barn lights or something but never said anything to me about it and didn't put it back the way I had it.

Well, I am pulling the breaker out today so that doesn't happen again!!!! Now I can see how terrible accidents could happen if you just don't double check.

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